1. Field of the Invention
The present invention relates to a network connection device and a network connection method for relaying data transfer between networks such as IEEE 1394 buses and radio networks, and a communication device for carrying out communications through a network such as IEEE 1394 bus and radio network.
2. Description of the Background Art
In recent years, the so called “digitalization of home AV environment” is attracting much attentions as exemplified by the beginning of the digital broadcasting and the sales of digital AV instruments. Digital AV data have some excellent characteristics including the fact that various compression schemes are applicable, the fact that they can be processed as multimedia data, the fact that they are not degraded no matter how many times they are playbacked, etc., so that they are expected to have even wider use in future.
However, this digital AV technique has another aspect that “an illegal copy of contents can be made easily”. Namely, for any digital contents, it is in principle possible to produce a copy with the same quality as the original, that will not degrade at all forever, by making “bit copy” so that the so called “illegal copy” problem arises.
Some techniques for preventing this “illegal copy” are currently discussed, including “1394CP Content Protection system Specification” that is discussed by the CPTWG (Copy Protection Technique Working Group). In this technique, for contents (such as MPEG data for example) to be transferred between nodes connected to the IEEE 1394 bus, the authentication between the transmitting and receiving nodes is carried out in advance so as to enable the sharing of an encryption key (contents key), and the contents are subsequently transferred by encrypting the contents such that the contents cannot be read by anyone except for those who have carried out the authentication procedure.
In this way, a node that has not carried out the authentication procedure cannot ascertain the value of the contents key so that even if the transferred data (encrypted data) are obtained by such a node, the encrypted data cannot be decrypted by such a node. By making a rule that nodes that can participate in the authentication are only those nodes that are permitted by a prescribed authentication authority, it is possible to prevent an illegal node from acquiring the encryption key so that it is possible to prevent the illegal copy.
The IEEE 1394 bus is a network system having some very excellent characteristics including the fact that its speed is 100 Mbps at least, the fact that the network itself is equipped with an automatic configuration recognition function, the fact that it has a QOS transfer function, etc., so that it has been established as the de facto standard of a network for home digital AV use.
However, because of these characteristics, the IEEE 1394 also give rise to various constraints in the case of “connecting the IEEE 1394 with other networks”. For example, in the case of connecting the IEEE 1394 bus with a radio network or a public network, it is impossible to directly extend the IEEE 1394 protocol to the radio network or the public network, because these networks are not as fast as over 100 Mbps in general and the automatic configuration recognition function of the IEEE 1394 cannot be directly extended to these networks so easily.
For this reason, there are some propositions including a method in which a protocol conversion gateway is provided between the IEEE 1394 and the other network such as radio network or public network so as to interconnect them, and a method using the so called proxy server for providing services on one network as services on the other network.
But, in the case of attempting to apply these methods to the 1394 copy protection described above, currently the copy protection technique is defined only for the IEEE 1394 bus and currently there is no technique for extending this copy protection technique to the case of “connecting the IEEE 1394 with the other network”.
Also, in the case of connecting the IEEE 1394 buses together, the following problems have been encountered.
In the case where a transmitting node connected to the IEEE 1394 bus transmits encrypted data, it will transmits a packet that contains at least the encrypted data, a source node ID, and a transmission channel.
In the case of transmitting this data to a receiving node connected to another IEEE 1394 bus that is connected with the transmitting side IEEE 1394 bus through a network connection device, the following two cases can be considered. In the first case, the network connection device rewrites the source of this packet to a node ID of the own device. In this case, there has been a problem that the transmitting node and the receiving node cannot carry out the authentication and key exchange directly. On the other hand, in the second case, the network connection device transfers data without rewriting the source node ID. In this case, there has been a problem that an overlap in the node ID occurs because the transmitting node and the receiving node are on different IEEE 1394 buses so that data cannot be transferred accurately.
Thus the conventional copy protection techniques are insufficient for an extension to a system in which the IEEE 1394 buses are connected together through a 1394 bridge.